I saw a TV show not too long ago which pointed out that there are still no-speed-limit zones on the Autobahn. The Autobahn isn't one big no-speed-limit zone anymore, however.
True, and there was, when I was there, a practical limit on speeding. In accidents above 130 Kph, (78), insurance may not pay off.
The only speed zones on the Autobahnen are in cities, at a few congested interchanges, construction zones, and in some curvy mountain areas.
Most of the road system has no speed limit, and is readily negotiable at 140 mph.
Personally, I never felt comfortable going more than 110-115 mph.
The German Police focus intensely on ticketing slow people clogging up the passing lane, rather than going after speed violations.
The Austrians, OTOH, love to run speed traps on their part of the Autobahnen, as do the Czechs. Both those countries limit their identically constructed roads to an artificially slow 80 mph. OTOH, the Austrians allow for relatively very high speeds on rural 2 lane roads - 75 mph if I remember from driving the road from Vienna to Brno, with passing on the opposite lane allowed the entire length of the road. The roads were built wide enough to allow this, and all the drivers are intelligent and courteous enough to allow it to work.
The Italian Autostrada are also good for very high speeds, and although apparently they do have speed limits, though they do not appear to be enforced from my visits there. Nearly everyone was driving 90-120 mph.
American speed limits and roads and traffic enforcement are a pathetic joke. It is amazing supposedly "free" Americans put up with the imposition, which is little more than outright highway robbery by the state.